The invention relates to a hydraulic switching valve which can open very fast from the closed position using a usual electric signal of very low energy.
Valves with these characteristics are known from the patent applications PCT/NL 96/00157 dated Apr. 10, 1996 and PCT/NL 95/00260 dated Jul. 27, 1995.
The application mentioned first is about a valve operated by a so-called adjusting piston which can move the valve body very fast after an electrical signal of low energy. Together with the adjusting cylinder the adjusting piston forms a first and a second displacement chamber in which in the first position the first and the second displacement chambers are connected to low pressure. From said first position the adjusting piston, apart from the spring force present, can move freely but after a small initial movement the first displacement chamber is connected by the adjusting piston to the high pressure Ph and as a result moves to the second position. The adjusting piston can drive a large variety of valve types with an almost unlimited number of switching functions. In case a simple on-off valve is driven a fast-working hydraulic switching valve is created. A drawback of said valve remains that through the gap sealings of the adjusting piston leakage occurs from the main supply with high pressure Ph, so that a tight hydraulic switching valve cannot be realized in this manner. In some of the known embodiments a relatively heavy valve spring is also necessary to keep the operated valve closed.
In PCT/NL95/00260 the valve body has two sealing edges, which with the valve casing in the closed position, form three chambers, the first chamber at all times being connected to the high supply pressure Ph, the second chamber in the closed position also being connected to the high pressure supply Ph, and the third chamber to the exit of the valve with exit pressure Pu. This outgoing pressure Pu can in principle be between Ph and the low system pressure Pl.
As a result of the in and outgoing pressure only, the valve will open spontaneously but can be kept in the closed position by high pressure Ph in the second chamber which is active on the second surface of the valve body which surface is larger than the first surface of the valve body in the first chamber on which the high pressure Ph is active.
The valve will open as soon as the second chamber is connected to low pressure Pl via switching means present. Because only very little liquid transport is needed to let the pressure drop sufficiently in the second chamber, it is about switching means of small passage which as a result can very quickly react to an electrical signal of low energy. As soon as the pressure in the second pressure chamber has dropped sufficiently the valve will open under influence of the pressure Ph on the first surface of the valve body.
A drawback of the valve from PCT/NL95/00260 is that the two seat sealings of the valve body in case of the intended tight embodiment have to close at exactly the same time and to that end have to comply with very high mechanic processing tolerances. In order to solve this problem the valve body in the preferred embodiment is built up from two parts that can move with respect to each other which parts are separated from each other via a gap sealing. This embodiment however increases the complexity, reduces the opening force (because a permanently active closing force under influence of the high pressure is created) and a leakage gap is created between the two valve parts.
A second drawback is that after opening a connection has been created between the high pressure supply and the low pressure Pl via the opened and electrically operated switching valve with which the second chamber is connected to low pressure. The period of time during which this electro valve has to remain opened is critical because for a switch of the hydraulic switching valve which is reliable and safe to operate, a certain minimal opening time is needed whereas on the other hand an opening time which is as short as possible is desired in order to prevent too much leakage loss via the opened electro valve to level Pl.
A third drawback of said switching valve is that it may close spontaneously for a longer or shorter period of time after a short pressure rise in the outgoing pipe to the level Ph. Such a pressure rise can easily arise by the closing of a present intermediate valve further down the outgoing pipe to for instance the hydro cylinder to be operated or by an occurring load of said cylinder. Because of the high pressure in the outgoing pipe pressure balance is created in the valve casing as a result of which the spring force will close the valve. When subsequently the load of the connected cylinder fails again or the intermediate valve is opened, Pu will drop fast and as a result the situation with high pressure in the first and second chamber and low pressure in the third chamber is created, and these are the same conditions which are maintained in the closed position using the electro valves in order to keep the valve closed.
In view of safety a drawback in some uses of this valve can also be the fact that the valve will open immediately when through unforeseen causes the high control pressure in the second chamber would fail for a moment. Without said control pressure in the second chamber commanded by the electro valves the valve acts as a non-return valve which spontaneously and immediately opens when there is pressure on the entrance of the valve.
The object of the invention is to provide an alternative for the fast-working hydraulic switching valve with which also the occurring drawbacks of the known switching valves can be prevented.
With regard to the valves moved by an adjusting piston described in PCT/NL96/00157 the hydraulic switching valve according to the invention distinguishes itself by the lack of the adjusting piston.
With regard to the valve from PCT/NL095/00260 described above, the valve according to the invention distinguishes itself because in the known configuration of valve and valve body the connections of the valve casing are changed in that sense that the third pressure chamber is at all times connected to the entrance 16 of the valve with high pressure Ph instead of with the exit pressure Pu, whereas in the closed position the first chamber is connected to low pressure instead of the high pressure Ph. Additionally in all embodiments switching means are present which can connect the first instead of the second chamber with high or low pressure. The design and dimensioning of the valve body here differ among others because the first surface 9c is larger than the second surface 10c instead of the other way round. The valve according to the invention further has two main embodiments.
In the first embodiment of FIG. 1 the second chamber 10 is permanently connected to the exit 17 of the valve with pressure Pu.
In the second embodiment the first chamber 9 is at all times connected to the exit 17 of the valve with pressure Pu and the second chamber 10 is at all times connected to the low pressure Ps2, the second sealing edge being designed as a gap sealing 10b to which tight seat sealing 10a is added. The embodiment being such that the gap sealing 10b seals permanently between the second and the third chamber 10 and 11.
In the new switching valve which is created in this way the drawbacks mentioned do not occur, which is elucidated in short below.
The leakage losses via the adjusting piston do not occur because the adjusting piston is not there. A very light valve spring is at all times sufficient here because in all cases the switching valve can be kept safely in the closed position even without spring force.
The leakage losses via the electric switching valve 1 to Pl do not occur because switching takes place from Pl to Ph takes place. The switching period therefore is no longer critical.
There is no possibility of a spontaneous closing of the hydraulic switching valve because in the first embodiment according to FIG. 1, from the position of pressure balance between Ph and Pu and a valve closed by the spring force, when the pressure Pu fails the closing force also fails which is exerted by the pressure Pu on the second surface 10c of the valve body. The failing of said closing force therefore means in this case that the resulting opening force on the valve body increases, as a result of which an unwanted spontaneous closing cannot occur.
In the embodiment according to FIG. 2 spontaneous closing does not occur either because for the closing the pressure Ps2 first has to become higher than the pressure in the entrance pipe 16 and this condition cannot spontaneously occur.
The measures as well which are described in PCT/NL95/00260 to realize a simultaneous tight closing of the seat sealings are not necessary in the hydraulic switching valve according to the invention. Instead the valve body is dimensioned such that it deforms elastically under influence of the pressure Ph in the third chamber on the valve body as a result of which both sealing edges will seal tightly.
The valve according to the invention is furthermore intrinsically safe because no pressure is needed in the first chamber to keep the valve closed. Also when the control pressure Ps fails or even when the valve spring breaks the valve according to the invention is still kept firmly closed under influence of the high entrance pressure Ph on the valve part 7a. 
Characterizing for the hydraulic switching valve according to the invention is that switching means (1 and 2) are present to connect the first chamber (9) to high or low pressure (Ph or Ps), said first chamber (9) in the closed position of the valve being connected to low pressure (Pl) and the third chamber (11) at all times being connected to the high entrance pressure (Ph) whereas the first surface (9c ) of the valve body is larger than or equal to the second surface (10c).